In the art of drip irrigation there are known end or plug emitters that are disposed at the outlet ends of branch irrigation pipes. They constitute plugs with some sort of pressure-reducing device providing slow trickling or dripping of water through the outlet end of the branch pipe. The branch pipe is connected by its other end to a main line supplying water under pressure.
GB 1,136,993, U.S. Pat. Nos. 3,833,176 and 3,840,209 disclose branch pipes made of resilient material with a threaded screw inserted in the outlet end of the pipe. The threads of the screw cut into the resilient walls of the branch pipe forming a restricted helical passage between the threads and the wall. The passage has great hydraulic resistance to the passing flow and thereby constitutes a pressure-reduction device. The rate of dripping may be regulated by drawing the screw deeper into the pipe or by withdrawing it.
U.S. Pat. No. 3,934,824 discloses an end emitter constituting a collapsible tube with a plurality of crimps or folds providing a sinuous path to the emitted water. The pressure reduction function of a particular end emitter is regulated by cutting off a part of the crimps.
U.S. Pat. No. 4,043,360 discloses a pressure reducing device suitable for use as an end dripper. The device has an inner cylindrical body with a plurality of transverse grooves interconnected in axial direction so as to form a tortuous flow labyrinth with the walls of a pipe where the cylindrical body is inserted.
In all the above examples, the emitters are designed for insertion in the pipe only through the end thereof.